Metal matrix composites of aluminum, magnesium and titanium using calcium hexaboride

ABSTRACT

A metal matrix composite was fabricated by adding particles of calcium hexaboride to a metal of aluminum, magnesium or titanium and their alloys. The resulting metal matrix composite is light weight has improved strength, increased elastic modulus and reduced thermal coefficient of expansion, thus making the metal matrix composite more useful in industry.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the improvedmechanical and physical properties including strength, elastic modulusand reduced thermal expansion of metal bodies by using metal matrixcomposites, and more particularly to the reinforcement of aluminum,magnesium and titanium by forming metal matrix composites of these metalusing calcium hexaboride particles.

BACKGROUND OF THE INVENTION

[0002] The light weight metals of aluminum and magnesium have very largemarkets for they are utilized in a wide variety of industries. In alesser way, titanium is also utilized as a light weight fabricationmaterial. These metals suffer from some drawbacks, however, which limittheir usefulness. These include low stiffness (low modulus ofelasticity), high thermal coefficient of expansion, and low strength.Some of these drawbacks have been overcome through the use of metalmatrix composites of these metals. Typically, ceramics are added to themetals. The primary objectives of these additives have been to increasethe modulus of elasticity and to reduce the thermal coefficient ofexpansion. When fibrous material, such as silicon carbide whiskers, areadded, strengthening has been observed. Other added materials includethe fibers of boron metal, carbon, aluminum silicate, and aluminumoxide. Still other typical strengthening agents are aluminum oxideparticulates, boron carbide and silicon carbide in various forms.

[0003] Of these, only aluminum oxide particulate and silicon carbideparticulate have been extensively utilized in the aluminum-based matrix.To add either of these to molten aluminum, a continuous stirring actionmust be utilized because the specific gravity of the additives aresignificantly greater than the molten aluminum. Similar problems wouldbe observed with molten magnesium. The continuous stirring causes oxideinclusions and hydrogen to contaminate the melts.

[0004] Furthermore, because of the contamination and the non-uniformnature of the metal matrix composites, remelting (for recycle, etc.) isa problem due to the variability of the resulting feed product.

OBJECTS OF THE INVENTION

[0005] Accordingly, it is an object of the present invention to providea metal matrix composite using molten metal of aluminum, magnesium andtitanium wherein a minimum of stirring is required to maintain particlesof the additive agent in suspension.

[0006] It is another object of the present invention to provide a metalmatrix composite wherein the strengthening agent has a specific gravitysimilar to that of the molten metal whereby there is little settling ofthe additive particles during the formation of the metal matrixcomposite.

[0007] It is a further object of the present invention to provide ametal matrix composite wherein the additive particles increases theductility of the metal matrix composite.

[0008] Further and other objects of the present invention will becomeapparent from the description contained herein.

SUMMARY OF THE INVENTION

[0009] In accordance with one aspect of the present invention, a new andimproved metal matrix composite comprises a metal matrix compositeformed from a molten metal selected from the group consisting ofaluminum, magnesium, titanium and mixtures thereof, and particles ofcalcium hexaboride. The amount of calcium hexaboride particles presentin the metal is in the range of about 0.1 to about 80 wt. %.

[0010] In accordance with another aspect of the present invention, a newand improved metal matrix composite comprises a metal matrix compositeformed from a molten metal selected from the group consisting ofaluminum, magnesium, titanium and mixtures thereof, and particles ofcalcium hexaboride and particles of silicon hexaboride. The amount ofparticles of calcium hexaboride and particles of silicon hexaboride inthe metal is in the range of about 0.1 to about 80 wt. %.

[0011] In accordance with another aspect of the present invention, a newand improved article of manufacture comprises a metal matrix composite.The metal matrix composite comprises a metal selected from the groupconsisting of aluminum, magnesium, titanium and mixtures thereof, andparticles of calcium hexaboride. The amount of particles of calciumhexaboride in the metal is in a range of about 0.1 to about 80 wt. %.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A metal matrix composite was fabricated by adding particles ofcalcium hexaboride to molten aluminum. The calcium hexaboride wassupplied by WACKER-CHEMIE of Kempten Germany. Since the specific gravityof the calcium hexaboride is very close to that of aluminum, only aminimal amount of stirring was required to achieve a homogeneousmixture. If heating is accomplished in an induction furnace, a stirringaction is automatically achieved. Some mechanical stirring is requiredunder other conditions of heating.

[0013] While a range of compositions of from about 0.1 wt. % to about 80wt. % of calcium hexaboride can be utilized relative to the aluminum, arange of about 5 to about 40 wt. % is most practical for mostapplications and was utilized for testing. The calcium hexaboridetypically has an average particle size range of about 0.1 to about 200microns. The resultant metal matrix is light weight has improvedstrength, increased ductility and reduced thermal coefficient ofexpansion.

[0014] The addition of the calcium hexaboride to the molten metal wasprincipally utilized in the development of the present invention.However, it will be understood that the invention also includes theblending of the calcium hexaboride particles with powdered aluminummetal and any other alloying constituents prior to melting the mixture.

[0015] In addition a mixture of calcium hexaboride particles and siliconhexaboride particles may be added to the molten metal. A siliconhexaboride prepared by a substantially commercial process can be usedand was comparable with that supplied by CERAC of Chicago, Ill. andtypically has an average particle size range of about 0.1 to about 200microns.

[0016] The molten mixture can be cast into a desired shape as amanufactured product, such as horseshoes, memory disk substrates,actuator arms for disk drives or any product which would benefit fromthe improved mechanical and physical properties of the metal matrixcomposite of this invention.

EXAMPLE 1

[0017] A metal matrix composite horseshoe was made from an aluminummatrix composite. The aluminum matrix composite contained from about 5to about 10 wt % calcium hexaboride particles having an average particlesize of about 75 microns and the remainder being A356 aluminum metal.The resulting horseshoe was light, strong, abrasion resistant andunexpectedly ductile. The horseshoe could be bent at an angle of 45degrees without damage.

EXAMPLE 2

[0018] A metal matrix composite memory disk substrate was made from analuminum matrix composite. The aluminum matrix composite contained fromabout 40 wt % calcium hexaboride particles having an average particlesize of about 10 microns and the remainder being aluminum metal. Theresulting memory disk substrate was light, strong, abrasion resistantand ductile.

EXAMPLE 3

[0019] A metal matrix composite actuator arm for a hard drive was madefrom an aluminum matrix composite. The aluminum matrix compositecontained about 30 wt % calcium hexaboride particles having an averageparticle size of about 50 microns and the remainder being A356 aluminummetal. The resulting actuator arm for a hard drive was light, strong,abrasion resistant and unexpectedly ductile.

[0020] An unexpected increase in ductility was observed in the productsmade by the addition of calcium hexaboride particles into the metalmatrix composites relative to other metal composites.

[0021] Magnesium and titanium have low specific gravities similar tothat of aluminum. Accordingly, metal matrix composites of these metalswith calcium hexaboride is within the scope of the present invention.

[0022] From the foregoing, it will be understood that improved metalmatrix composites of aluminum, magnesium and titanium are achieved bythe addition of calcium hexaboride particles. The composition can beeasily prepared with a minimum of stirring, and the product can berecycled if desired.

[0023] While there has been shown and described what is at presentconsidered the preferred embodiments of the invention, it will beobvious to those skilled in the art that various changes andmodifications may be made therein without departing from the scope ofthe invention as defined by the appended claims.

I claim:
 1. A metal matrix composite comprising a metal selected fromthe group consisting of aluminum, magnesium, titanium and mixturesthereof, and particles of calcium hexaboride, said particles of calciumhexaboride being present in a range of about 0.1 to about 80 wt. % inthe metal.
 2. A metal matrix composite in accordance with claim 1wherein said calcium hexaboride has an average particle size of about0.1 to about 200 microns.
 3. A metal matrix composite in accordance withclaim 1 wherein said metal is aluminum.
 4. A metal matrix compositecomprising a metal selected from the group consisting of aluminum,magnesium, titanium and mixtures thereof, and particles of calciumhexaboride and particles of silicon hexaboride, said particles ofcalcium hexaboride and said particles of silicon hexaboride beingpresent in a range of about 0.1 to about 80 wt. % in the metal.
 5. Ametal matrix composite in accordance with claim 4 wherein said particlesof calcium hexaboride and said particles of silicon hexaboride have anaverage particle size of about 0.1 to about 200 microns.
 6. A metalmatrix composite in accordance with claim 4 wherein said metal isaluminum.
 7. An article of manufacture comprising a metal matrixcomposite, said metal matrix composite comprises a metal selected fromthe group consisting of aluminum, magnesium, titanium and mixturesthereof, and particles of calcium hexaboride, said particles of calciumhexaboride are present in a range of about 0.1 to about 80 wt. % in themetal.
 8. An article of manufacture in accordance with claim 7 whereinsaid calcium hexaboride has an average particle size of about 0.1 toabout 200 microns.
 9. An article of manufacture in accordance with claim7 wherein said metal is aluminum.
 10. An article of manufacture inaccordance with claim 7 wherein said article of manufacture is ahorseshoe.
 11. An article of manufacture in accordance with claim 10wherein said horseshoe was made from an aluminum matrix composite, saidaluminum matrix composite containing from about 5 to about 10 wt %calcium hexaboride particles having an average particle size of about 75microns and the remainder being A356 aluminum metal.
 12. An article ofmanufacture in accordance with claim 7 wherein said article ofmanufacture is a memory disk substrate.
 13. An article of manufacture inaccordance with claim 12 wherein said memory disk substrate was madefrom an aluminum matrix composite, said aluminum matrix compositecontaining from about 40 wt % calcium hexaboride particles having anaverage particle size of about 10 microns and the remainder beingaluminum metal.
 14. An article of manufacture in accordance with claim 7wherein said article of manufacture is an actuator arm for a hard drive.15. An article of manufacture in accordance with claim 14 wherein saidactuator arm for a hard drive was made from an aluminum matrixcomposite, said aluminum matrix composite containing from about 30 wt %calcium hexaboride particles having an average particle size of about 50microns and the remainder being A356 aluminum metal.